The present invention relates to a compressed air filter assembly for a nail gun, and more particularly to an air filter unit installed at an end cap of a handle of a nail gun, capable of filtering dust or the like in the compressed air guided into a main air chamber of the nail gun.
As generally known, a handle of a typical nail gun has a main air chamber, the compressed air being guided therein through an inlet port of an end cap disposed at a tail end of the handle. The compressed air is accommodated in a gun body of the nail gun, as a power source of driving a piston. In addition, the inlet port extends into the main air chamber to form an inlet pipe, and a filter is provided between the main air chamber and the inlet port for preventing dust or the like from entering inside. The filter is generally made from soft cotton or unwoven cloth.
As shown in U.S. Pat. No. 5,259,465, U.S. Pat. No. 6,517,593, U.S. Pat. No. 6,726,080 and U.S. Pat. No. 7,122,066, a filter is provided between the inlet port of the end cap and the main air chamber of the handle, for filtering the impurities in the compressed air.
However, the fixing way of the filter between the end cap and the handle makes the filter to easily fall off in the process of assembling or disassembling the end cap. Thus, the filter is easy to be affected with damp or be defiled. In addition, the filter is easy to be deformed under a rotating force provided on the end cap, which reduces the filtration capacity of the filter. Moreover, after a period of usage, the center portion of the filter being blasted by the compressed air is easy to produce distortion, which lowers the usage life of the filter.
To resolve above described questions, TW Pat. No. M269157 discloses a technology of locating a filter at the inlet pipe. As shown in FIG. 9, an inlet pipe 21a of an end cap 2a disposed at a tail end of a handle 1a has a ring-shaped step 22a and a ring-shaped groove 25a formed on an inner peripheral surface. A filter 3a is set in the inlet pipe 21a. The ring-shaped groove 25a has a ring-shaped fastener 8, and the filter 3a is fixed between the fastener 8 and the step 22a. That is, the filter 3a is located between a main air chamber 10a of the handle 1a and an inlet port 20a. However, the technology still has the question of a center portion 31a of the filter 3a being distorted under long time blasting of the compressed air, which lowers the usage life of the filter 3a. 
Furthermore, U.S. Pat. No. 5,637,125 and U.S. Pat. No. 20060162302 also disclose a technology of screwing a cylindraceous filter device having a filter therein at an inlet pipe, which is used to filter the compressed air being guided into the main air chamber through the inlet pipe. However, the cylindraceous filter device makes the structure more complex comparing to the above described structure having a single filter. Thus, the cost is increased.
Accordingly, what is needed is a compressed air filter assembly for nail gun that can overcome the above-described deficiencies.